1. Field of the Invention
The invention generally relates to joint prosthesis devices and, more specifically, involves a wrist joint prosthesis for human implantation and use.
2. Description of the Prior Art
Although wrist joint prosthetic devices have been proposed in the prior art, they have not always been entirely successful. This is due to the fact that the wrist joint is relatively more complex than most joints in that it comprises a greater number of bones which cooperate to provide a plurality of distributed articular capabilities.
Insofar as the wrist joint is regarded as being one of the more likely joints to be affected by arthritic conditions which reduce articular function, the need for effective wrist joint prosthesis is great. Further, a wrist joint prosthesis can be used to replace a wrist joint which does not provide complete function or otherwise adversely affects the entire wrist and utility of the relevant hand.
The Meuli design for a wrist joint prosthesis is a ball-and-socket joint. The distal component of the Meuli prosthesis consists of a hemispherical cup with two attached stems that fit through the remnant of the carpal row into the second and third metacarpals. The proximal component consists of a single peg at the wrist level with two stems that insert into the radial intermedullary cavity. A polyethylene ball is placed on the peg and is reduced into the distal hemispherical cup, providing a range of motion in flexion, extensions, abduction, adduction, and rotation. The rotation is not entirely desirable. The stems of the proximal and distal components are malleable so that they may be adjusted.
Another prosthesis, by Voltz, has only two degrees of freedom and thus behaves as a universal joint. Flexion and extension occur in one plane, and radial abduction and ulnar abduction occur in the second plane. This is somewhat more physiologic but causes additional difficulties in design.